MAX1856EUB+T Maxim Integrated Products, MAX1856EUB+T Datasheet - Page 12

• Manufacturer Part Number: MAX1856EUB+T
• Description: IC PWR SPLY PWM SLIC 10-UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX1856EUB+T

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 575kHz
• Duty Cycle: 94%
• Voltage - Supply: 3 V ~ 28 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: Yes
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 85°C
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Frequency-max: 575kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Wide Input Range, Synchronizable,
PWM SLIC Power Supply
Table 1. Transformer Selection for Standard Applications
Table 2. Transformer Suppliers
gives 1.11A for 80% efficiency. With a duty cycle of
52.5%, the average switch current (I
Choosing a primary inductance ripple current ∆I
40% of the average switch current, the primary induc-
tance is given by:
Selecting f
0.846A, the primary inductance value is 27µH, and the
peak primary current for this example is therefore 2.5A.
The transformer in a flyback converter is a coupled
inductor with multiple windings on the same magnetic
core. Flyback topologies operate by storing energy in
the transformer magnetics during the on-time and
transferring this energy to the output during the off-
time.
Core selection depends on the core’s power-handling
capability. The required output power is first consid-
ered. For example, the standard application circuit
requires 9.6W. Assuming a typical 80% efficiency, the
transformer must support 12W of power. The core
material’s properties, the core’s shape, and the size of
the air gap determine the core’s power rating. Since the
equations relating these properties to the power capa-
bility are involved, manufacturers simply provide charts
giving “Power vs. Frequency” for different core sizes.
12
Coilcraft
Coiltronics
ICE Components
Pulse Engineering
TDK
INPUT VOLTS (V)
______________________________________________________________________________________
VENDOR
12
12
12
OSC
5
= 250kHz and ∆I
L
P
=
∆ ƒ
I
L OSC
V D
IN
OUTPUT VOLTS (V)
-24 and -72
-95 and -30
L
-48
-48
= 0.4 x I
SW(AVG)
847-639-6400
888-414-2645
800-729-2099
858-674-8100
847-390-4461
USA PHONE
Core Selection
) is 2.114A.
SW(AVG)
L
OUTPUT CURRENT (mA)
to be
=
320 and 150
400 or 100
100
100
For the standard application circuit (f
the EFD15 core from Coiltronics meets the criteria.
Once the core is chosen, the number of turns in the pri-
mary is given by:
where A
ber of ampere-turns (N
limit. A significant portion of the total energy is stored in
the air gap. Therefore, the larger the air gap, the lower
the A
at which saturation starts. Some manufacturers define
saturation as the current at which the inductance
decreases by 30%.
Once the peak inductor current is determined, the cur-
rent-sense resistor (R
Kelvin-sensing should be used to connect CS and
PGND to R
ground side of R
Due to inductive ringing after the MOSFET turns on, a
lowpass filter may be required between R
prevent the noise from tripping the current-sense com-
parator. Connect a 100Ω resistor between CS and the
L
847-639-1469
561-241-9339
703-257-7547
858-674-8262
847-390-4405
value and the larger the number of ampere-turns
USA FAX
L
is the inductance factor. Ensure that the num-
CS
R
Current-Sense Resistor Selection
. Connect PGND and GND together at the
CS
CS
VP3-0055 (Coiltronics)
CTX01-14853 (Coiltronics), or
ICA-0635 (ICE Components)
CTX01-14853 (Coiltronics), or
ICA-0635 (ICE Components)
CTX03-15220 (Coiltronics)
=
V
.
N
I
CS MIN
LPEAK
P
CS
=
(
TRANSFORMER (VENDOR)
) is determined by:
P
I
A
L
SAT
)
P
L
=
www.icecomponents.com
) is below the saturation
85
www.coiltronics.com
mV I
www.pulseeng.com
www.coilcraft.com
www.tdk.com
/
INTERNET
LPEAK
OSC
CS
= 250kHz),
and CS to